Process for the catalytic hydrogenation of carboxylic acid substances to amines



Patented Nov. 26, 1940 UNITED STATES PROCESS FOR THE CATALYTIC HYDROGEN-ATION OF CARBGXYLIC ACID SUBSTANCES TO AMINES Wilbur A. Lazier, NewCastle County, Del, assignor to E. I. du Pont de Nemours & Company,Wilmington, Del., a corporation oi. Delaware No Drawing. ApplicationApril 12, 1939,

Serial No. 267,448 r 6' Claims.

This invention relates to catalytic processes for the production oforganic amines. More particularly, it relates to a process for theproduction of amines by the catalytic hydrogenationof carboxylic acids,their esters, and their anhydrides in intimate association with ammoniaand its alkylated and arylated derivatives. Specifically this inventionrelates to and has as its principal object the application .of catalytichydrogenation to the formation of amines and other reduced nitrogencompounds from acid amides and acid imides.

This application is a continuation in part of copending applicationsSerial No. 742,476 filed September 1, 1934, which matured into U. S.Patent No. 2,187,745, and Serial No. 584,574 filed January 2, 1932.

The preparation of amines by organic chemical methods as from thealcohols or alkyl halides,

for example, is well known. Several attempts have been made with varyingdegrees of success, to effect the chemical reduction of amides toamines. Reports in the technical literature are contradictory as regardsthe yields obtainable 25 when employing sodium in absolute alcohol asthe reducing agent. The direct catalytic reduction of amides andammonium salts with hydrogen appears to be a particularly diflicultprocedure. Although Mailhe (Bull. soc. chim. (3)

35, 614 (1906)) obtained evidence of the formation of low molecularweight amines by passing the vapor of acetamide and hydrogen over anickel catalyst at atmospheric pressure, the yields have not beenrecorded and the work has not, to

35 my knowledge, been duplicated. The failure of other investigators toobtain technically successful yields of amines from amides is furtherevidenced by the factthat the amines corresponding to the common highmolecular weight acids, although of value in the arts, have never becomecommercially available.

This invention has as-an' object the production of organic amines by thecatalytic hydrogena- 4 tion of carboxylic acid substances such as acidamides, imides, and mixtures of carboxylic acids, their esters, or theiranhydrides with ammonia and its alkylated or arylated derivatives. Astill further object is the production of amines from 50 carboxylic acidsubstances having at least six carbon atoms. Another object is theproduction of amines from dicarboxylic acid substances having at leastsix carbon atoms. A further object is the production of amines fromadipic acid 55 substances.

Other objects will be apparent from I a reading of the followingdescription of the invention.

These objects are accomplished by the following invention, which in itsgeneral aspects comprises heating the compound to be hydrogenated in a 5suitable autoclave or higli pressure tube, together with an excess ofhydrogen, in contact with a suitable hydrogenation catalyst at elevatedtemperatures and pressures; or by permitting the compound to beconverted, admixed 10 with. excess hydrogen, to flow over ahydrogenation catalyst in a continuous manner in either the liquid orvapor phase. More specifically the objects are accomplished by bringinga mixture of a carboxylic acid substance having at least six 16 carbonatoms together .with hydrogen and a member selected from the groupconsisting of ammonia, primary and secondary amines into contact with acombined hydrogenation-dehydration catalyst at a temperature betweenabout 20 200 C. and about 450 C. and under a. pressure in excess of i0atmospheres.

The following examples illustrate in detail the preferred embodiments ofthe invention without limiting the invention thereto.

Example I A hydrogenation catalyst was prepared as follows: 23 grams ofcadmium nitrate, 24 grams of copper nitrate, and 243 grams of zincnitrate were dissolved in 500 cc. of water and mixed at ordinarytemperature with an equal volume of water containing 126 grams ofammonium bichromate and '75 cc. of 28% ammonium hydroxide. Afterstirring, the mixture was exactly neutralized with additional ammoniumhydroxide and allowed to settle. After several washes by decantation,the precipitate was dried, ignited at 400 C. and compressed into tabletsor grains suitable for use in a catalytic gas apparatus. 40

One hundred cubic centimeters of this catalyst was placed in a highpressure tube and heated to 390 C. At this temperature and at a pressureof 3000 lbs. per sq. in. 400 cc. of acetanilide (20% solution inaniline) was pumped over the catalyst together with an excess ofhydrogen flowing at the rate of about 10 cu. ft. per hour. The liquidreaction productswere condensed under pressure, separated from theexcess gas and distilled. A yield of 25% of mono-ethyl aniline wasobtained.

Example II A copper chromite hydrogenation catalyst was prepared bydissolving 428 grams of copper nitrate and 176 grams 0! chromicanhydrlde (ClOa) in 2750 cc. of water. To this solution grams ofanhydrous ammonia was added with stirring in order to precipitatecopper-ammonium chromate. The precipitate was filtered, dried, ignitedat 425 to 450 C. and then extracted with 10% acetic acid solution. Afterwashing and drying, the metallic chromite catalyst was screened 18 meshand was ready for use in the hydrogenation of amides. 4

Twelve grams of this catalyst, 75 grams 0! lauramide and 150 grams ofdecahydronaphthalene were placed in a steel autoclave and heated to 270C. with agitation under 3000 to 4000 lbs. per sq. in. hydrogen pressurefor 6 hours, the pressure being maintained by occasional fresh addition01 gaseous hydrogen. The tube was then cooled and the pressure released.After pouring out the contents, the tube was thoroughly washed withalcohol. The solution was then filtered to remove the catalyst and thealcohol distilled oil at atmospheric pressure. The decahydronaphthalenewas next distilled at 30 mm. pressure, boiling under these conditions atto C. After all of the hydrocarbon had been removed, the pressure of thedistillation was lowered to 2 mm., whereupon monododecylamine (M. P. 22to 25 C.) distilled over at 95 to C. The still residue was cooled,dissolved in ether, and treated with a stream of dry HCl gas.Didodecylamine hydrochloride was thus precipitated very rapidly, and wasfiltered off, washed with warm ether, dried, and then treated withaqueous alkali to liberate the free amine (M. P. 55 C.). From a typicalrun there was isolated 21 grams (30% yield) of monododecylamine and 29.5grams of didodecylamine hydrochloride (equivalent to a 40% yield ofdldodecylamine). The remainder consisted of a small amount of unchangedlauramide, a little dodecyl lauramide, and probably sometridodecylamine.-

Ewample III A composite hydrogenation catalyst was prepared as follows:To a solution consisting oil 52 grams of barium nitrate and 436 grams ofcopper nitrate trlhydrate dissolved in 1600 cc. of water, there wasadded with stirring a second solution consisting of 252 grams ofammonium bichromate and 300 cc. of 28% ammonium hydroxide dissolved in1200 cc. of water. The precipitate of mixed chromate's was filtered,dried, and ignited at 400 C. for 4 hours. The resulting mixed shaking.There was obtained a 30% yield of,

dodecylamine and a55% yield of didodecylamine.

Example IV Seventy-five grams of dodecyl lauramide, grams or dioxane,and 12 grams of the copper chromite catalyst prepared as described inExample 11. were heated to 250 to 260 C. in a steel shaker-tube under ahydrogen pressure of 3000 lbs. per sq. in. for 4 hours while maintainingconstant agitation. After cooling and filtering out the catalyst thesolution was evaporated to dryness and the residue recrystallized from500 acaaaos cc. of ethyl alcohol. By this procedure. there was obtained46.5 grams of didodecylamine corresponding to a 64.5% yield ofcalculated on the dodecyl lauramide used.

Example V The contents of a shaker-tube consisting of '75 grams ofcapric acid (3. P.154.to C. per 20 mm.) 150 grams ofdecahydronaphthalene, 10 grams of anhydrous ammonia, and 12 grams of thecopper chromite catalyst described in Example II, were heated withshaking at 260 to 270 C. under 4000 lbs. per sq; in. hydrogen pressurefor 4 hours. After filtering out the catalyst, the reaction mixture wasvacuum distilled. The fraction boiling between 95 to 120 C. per 30 mm.readily formed a solid hydrochloride in anhydrous hydrocarbon solventsin an amount corresponding to a 15% yield of decylamine.

Example VI The following mixture was charged into an alloy steel tube:75 grams of ammonium laurate (prepared from lauric acid and anhydrousam- 25 lbs. per sq. in. had been reached. After shaking the reactionmixture for 7 hours at a relatively constant temperature and pressure,the tube was cooled and its contents discharged. The catalyst wasremoved by filtration, and on distillation there was found 23% ofmonododecylamine.

Treatment of the still residue dissolved in ether with dry HCl gas gave5% to 10% of didodecylamine hydrochloride.

Example VII Seventy-five grams of lauramide, 150 grams of mineral oil(pharmaceutical grade) and 12 grams of the copper-barium-chromitecatalyst described in Example III were placed in a steel shaker-tube andheated to 270 C. under a hydrogen pressure of 3000 to 4000 lbs. per sq.in. After 7 hours of shaking at the above-mentioned temperature andpressure, the tube was cooled and the reaction mixture removed. Afterfiltering oil the catalyst, distillation gave 9-grams (13%) ofdodecylamine.

Example VIII Seventy-two grams of adipamide, 10 grams of an activecobalt-on-alumina catalyst, and 35 grams of ammonia were charged into asteel shaker-tube, and hydrogenation was allowed to proceed at 260 C.,and a total pressure of 500 to 700 atmospheres. The absorption amountedto about 'atmospheres in three hours. The tube was then cooled to roomtemperature and its contents discharged. The catalyst was removed fromthe liquid product by filtration. The latter was then fractionallydistilled giving 7.6 grams of hexamethylene diamine (13 per cent yield),B. 1?. 88 to 90 C./17 mm. There was also isolated a 7.3 per cent yieldof hexamethylene-imine, 7.5 grams of amines boiling higher than thediamine, and a non-volatile portion of 27 grams, which appeared to be amaterial of polymeric nature.

The present invention is applicable to the hydrogenation of a widevariety of acid amides to the corresponding amines, and contemplatestheCase I.

In this case, I have simple acid amides wherein R is either an alkyl oraryl radical of at least six carbon atoms. When R is an alkyl group, itmay contain one or more carbon atoms fully saturated with hydrogen orcontaining some unsaturated linkages. Representative compounds fallingunder Case I are caproyl amide, lauramide, benzamide, stearamide, oleylamide, etc.

Case II.

R is defined as in Case I and R1 may be either 'a group of aliphaticcharacter such as cyclohexyl, ethyl, methyl, dodecyl, etc., or an arylgroup such as phenyl, tolyl, benzyl, etc. Acetanilide, dodecyllauramide, etc., are typical amides which in this case are hydrogenatedto the corresponding sec-,

ondary amines.

Case III.

R 2Il-+RCHz-N +1150 Case IV.

70 where R may be an aryl, or alkyl grouping containing at least sixcarbon atoms, and R1 may be a hydrogen atom, or an alkyl or aryl group.Typical examples of imides falling under this case are phthalimide,wherein R is aromatic, and

75 substituted succinimides, wherein R is aliphatic.

it is also possible according to the present invention to convertdiamides such as Case V.

o-mn cumin R +4m--n +2mo o -mn cumin in cases where the structure of thecompound is such that ring formation does not take place readily. Herealso the hydrogen attached to the nitrogen atoms can be replaced by arylor alkyl groups, giving combinations similar to those obtainable in thecase of the monocarboxylic acids illustrated above. It should be noted,however, that a great number of these diamides at the temperature ofhydrogenation lose ammonia and form the cyclic imides, which onhydrogenation result in the formation of heterocyclic lactams andheterocyclic amines.

Instead of starting with preformed amides, I may as an alternative usefor the hydrogenation the free mono or dicarboxylic acids in thepresence of suflicient ammonia to give the ammonium salts which are thenconverted to the corre sponding amines, presumably through the amide asan intermediate stage. Instead of ammonia the alkyl or aryl derivativesof ammonia such as methylamine, diethylamine, aniline, etc., may beused. These ammonium salts or substituted ammonium salts may be preparedas pure compounds and then hydrogenated, or the necessary primaryingredients maybe mixed with the catalyst and hydrogenated at suitabletemperatures and pressures.

Furthermore, in place of the free acid, the derivatives of the acidssuch as the esters and anhydrides, may be mixed with ammonia or itsalkylated or arylated derivatives and then hydrogenated. Suitable estersfor hydrogenation in the presence of ammonia or amines include thesimple esters such as methyl adipate, ethyl stearate, ethyl benzoate,etc., and the naturally occurring glycerides such as coconut oil, cornoil, sperm oil, olein, etc. Whenever the hydrogenation process includesthefree acid, the ester of the acid, or the acid anhydride in admixturewith. ammonia, an exact chemical equivalent of ammonia or an excess ofammonia can be used. It has been found preferable, however, to employammonia in excess when a high yield of primary amine is desired.Furthermore, the addition of a reasonable excess of ammonia to thehydrogenation mixture, even in the case of a pur preformed amide, aidsmaterially in the formation of a high yield of the primary amine,because it lessens the tendency of the amine formed to react with itselfor unchanged amide with the evolution of free ammonia. The amount ofammonia in excess may vary from as low as 5% to as much as 1000%. Anaverage preferred value is approximately 100% excess of ammonia sincesmaller amounts fail to produce thedesired effects and appreciablylarger amounts decrease the partial pressure of hydrogen in the closedhydrogenation system to such an extent that hydrogenation proceeds onlyvery slowly. As in the case of acid hydrogenation, either an ester or analcohol may be formed, depending on the degree of hydrogenation; so inthe case of amide hydrogenation the conditions may be regulated to giveeither a substituted amide or an amine from a simple unsubstituted acidamide.

In the present invention it is preferable to use a solvent which willnot react with any of the materials employed in the process and will notbe effected by hydrogenation catalysts at high tem- 6 peratures andpressures. However, the reduction may be carried out in the absence of asolvent with a lower yield of primary amines and increased yields ofsubstituted amides and secondary and tertiary amines. The tendency of 10amines to react with themselves in the presence of hydrogenationcatalysts is well known and this reaction is favored in the absence of asolvent. As solvents, an inert water-miscible solvent such as dioxanemay be used. Other ethers such as -dibutyl ether and the alkyl ethers ofethylene glycol, and cyclic and straight chain hydrocarbons may also beused as suitable solvents. Alcohols, although operable, are notgenerally desirable because of the tendency to form 30 'alkylated aminesby the reaction of the amines formed and the alcohol employed as asolvent. The preferred solvent is decahydronaphthalene, although otherhydrocarbon solvents such as benzene, toluene, cyclohexane, water-whitemin- 25 eral oil, and other fractions of paraiiin hydrocarbons may beused with good results.

Depending upon the particular materials used and the degree ofhydrogenation desired, the processes of the present invention may becarried 30 out either in a liquid phase static system or in a vapor orliquid phase system suitably adapted to continuous flow. The temperatureemployed may vary from 200 to 450 0., with a preferred temperature rangeof 240 to 325 C. The hydrogen pressure should be in excess of 10atmospheres and preferably in excess of 100 atmospheres. It is likewisedesirable to employ a reasonable excess of hydrogen during thehydrogenation process; for example, in the condotinuous process a molalexcess of from 2 to 10 times the theoretical amount is convenientlyemployed.

The catalysts found suitable for carrying out this invention are thosewhich may be designated as hydrogenation-dehydration catalysts. Thesemay consist of a hydrogenating component such as hydrogenating metals ormetal oxides together with a dehydration component such as thosecompounds technically known as dehydration catalysts. As examples ofhydrogenation components there are such reduced metals as silver,copper, tin, cadmium, lead, iron, cobalt and nickel. These metalliccatalysts may be promoted with oxide promoters such as manganese 55oxide, zinc oxide, magnesium oxide, or chromium oxide. The promotedcatalysts may be physical mixtures or chemical compounds. The metalliccatalysts in the form of a powder may be used. The dehydration componentmay be any of the 60 well known dehydration catalysts; for example,

alumina, silica, thoria, kaolin, blue oxide of tungsten, etc. They maybe in the form of supporting material for the catalyst. An illustrationof such a catalyst is found in Example VIII where 65 cobalt is supportedon alumina.

Certain metallic oxides belong to the class of compounds known asdiflicultly reducible oxides and have both hydrogenating and dehydrationproperties. These two come clearly within the 70 class of catalysts thatmay be used in this invention. By the term diflicultly reducible ismeant that the oxides are not substantially reduced to metal byprolonged exposure in a state of purity to the action of hydrogen atatmos- 76 pheric pressure and at a temperature of 400 to 450 C. Suchoxides suitable for the hydrogenation of amides are zinc oxide,manganese oxide, magnesium oxide, etc. These oxides may beemployedeither alone or in combination with each other or with other oxideswhich have a promoting' action. Preferably the oxide employed as 'apromoter for the hydrogenating oxide has little activity of itself or ismuch less active than the hydrogenating oxide employed with it, but ityet serves to further promote the activity of the more active oxide.

It will be noted that the hydrogenating oxides are, in general, of abasic character. The promoting oxides are preferably chosen from thegroup consisting of the more acidic oxides of elements selected from thehigher groups of the Periodic Table. For example, the oxides ofchromium, vanadium, tungsten, titanium, and molybdenum are suitablepromoters for nickel, copper, cobalt, zinc oxide or manganese oxide. Ofthese, chromium oxide is preferred, since it inhibits to a greaterextent the tendency towards catalyzing destructive side reactions. Ihave found it advantageous to use chromium oxide in physical admixtureor in chemical combination, e. g., as a chromate or chromite, with alarge number of oxides ordinarily regarded as easily reducible. Theacidic promoting oxides other than chromium oxide may also be usedeither in physical admixture or in chemical combination, Q e. g., astungstates, vanadates, molybdates, etc. The reducible oxides such ascopper oxide, when combined or otherwise associated with chromiumoxides, are only partially reduced under conditions of operation and arefound to be very effective catalysts for the hydrogenation of amides toamines. Catalysts consisting of both reduced metals and non-reducedoxides are active even though the reaction is carried out at atemperature above the fusion point of the metal. Such 40 mixed catalystsare conveniently employed initially in the form of chromates orchromites of the metals. Manganese oxide-chromium oxide mixtures arealso suitable as well as copper oxide in combination with chromium oxideor other acidic oxides.

As indicated in the examples success has attended the use of mixtures ofthe chromites of two or more hydrogenating materials. The multiplechromite catalyst compositions described in the examples and disclosedin my application Serial No. 470,238, filed July 23, 1930, are eminentlysuited to use in the present invention. The multiple chromite catalystcompositions described in said application may be prepared by 5precipitation of a mixture of chromates from solution by adding analkali metal chromate to an aqueous solution of a mixture ofhydrogenating metal salts, followed by ignition or by high temperaturetreatment with hydrogen. In conducting the hydrogenation of amides bythe continuous vapor phase method, I prefer to use a chromitecomposition consisting substantially of zinc chromite but containinglesser quantities of the chromates or chromites of copper and cadmium.The activity of chromite catalysts may be further enhanced by subjectingthe ignited chromites to an acid extraction process which serves toremove from the composition a portion of the hydrogenating metallicoxide which is not combined with the promoter oxide.

The advantages attending the use of diflicultly reducible oxides orreducible oxides in a difficultly reducible form are several andsubstantial.

These'catalysts possess a high activity and are sturdy in character.They are relatively immune to degenerative'processes such as sinteringand poisoning, being thus distinguished from metal catalysts whichdeteriorate rapidly when subjected to excessive heating.

I wish to make special mention of the utility of catalysts containingcopper oxide promoted by chromium oxide either in physical mixture or inchemical combination as copper chromate or copper chromite. useful forliquid phase amide hydrogenation reactions. The conventional type ofsupported reduced ferrous metal catalysts, especially those containingnickel, are also eminently suited to the hydrogenation of amides toamines by the liquid phase batch method.

The catalysts described above may be further modified or promoted by theaddition of oxides or carbonates of alkali metals or of alkaline earthmetals, or of basic compounds of alkali metals or of alkaline earthmetals, for example, barium hydroxide, sodium carbonate, calciumcarbonate, and magnesium oxide. Other suitable promoters are compoundscontaining-an alkali or alkaline earth metal combined with the acidradical of an oxygen-containing acid, e. g., barium chromate.

In carrying out the processes of this invention, I may use from 2% to10% by Weight of catalyst, depending upon the specific catalystcomposition, the particular type of equipment used and upon otherconditions such as temperature and pressure.

Prior to the discovery of the processes of the present invention theamines corresponding to the acids found in the naturally occurring fatshave been more or less laboratory curiosities and have been prepared inlow yields only by tedius processes involving a large number of chemicalsteps. By means of the novel methods herein described these amines, aswell as numerous other organic amines, have now been made readilyavailable for important applications in the arts.

As many apparently widely difierent embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that I do not limit myself to the specificembodiments-thereof except as defined in the appended patent claims.

This catalyst is particularly.

I claim:

1. The process of producing amines which comprises bringing a mixture ofa carboxylic acid substance having at least six carbon atoms therein,hydrogen, and a member from the group consisting of ammonia, primary andsecondary amines, into contact with a combined hydrogenation-dehydrationcatalyst at a temperature between about 200 C. and about 450 C. and. ata pressure in excess of 10 atmospheres.

2. The process in accordance with claim 1 characterized in that thereaction is carried out comprises bringing a mixture comprising a di- 2carboxylic acid substance having at least six carbon atoms therein,hydrogen, and a member of the group consisting of ammonia, primary andsecondary amines, into contact with a combined hydrogenation dehydrationcatalyst at a temperature between 200 and 450 -C. and at a pressure inexcess of 10 atmospheres.

5. The process which comprises bringing a mixture of adipic acid,hydrogen, and a member of the group consisting of ammonia, primary andsecondary amines into contact with a combined hydrogenation-dehydrationcatalyst at a temperature between about 200 and about 450 C. and at apressure in excess of 10 atmospheres.

6. The process which comprises bringing a mixture comprising adipamide,hydrogen and a member of the group consisting of ammonia, primary and.secondary amines into contact with a hydrogenation catalyst at atemperature between about 200 and about 450 C. and at a pressure inexcess of 10 atmospheres.

WILBUR A. LAZIER.

